Objective To identify differential genes between normal ovarian epithelium tissue and ovarian epithelial cancer using representational difference analysis of cDNA （cDNA-RDA）. Methods cDNA-RDA was performed to identify the differentially expressed sequences between cDNAs from cancer tissue and cDNAs from normal ovarian tissue in the same patient who was in the early stage of ovarian serous cystadeno- carcinoma. These differentially expressed fragments were cloned and analyzed

then sequenced and compared with known genes. Results Three differentially expressed cDNA fragments were isolated using cDNA from normal ovarian tissue as tester and cDNA from cancer tissue as driver amplicon by cDNA-RDA. DPⅢ-1 and DPⅢ-2 cDNA clone showed significant ho- mology to the cDNA of alpha actin gene; DPⅢ-3 cDNA clone showed significant homology to the cDNA of transgelin gene. Conclusion cDNA-RDA can be used to sensitively identify the differentially expressed genes in ovarian serous cys- tadenocarcinoma. Ovarian serous cystadenocarcinoma involves alteration of multiple genes.